Zinc alloy engraving plate



Patented Dec. 27, 1938 UNITED STATES PATENT OFFIQE ZINC ALLOY ENGRAVINGPLATE setts No Drawing. Application September 18, 1936, Serial No.101,530

Claims.

This invention relates to zinc sheets used in the graphic arts industry,such, for example, as rolled zinc plates used for photo-engraving.

'Zinc sheets in various thicknesses are used in 5 the graphic artseither as photo-engraving plates (zinc etchings), or as lithographerssheets. In the first instance the plates must have one surface carefullyground and polished on which the photo-engraver develops the desiredimage in relief by the well known processes of photography and etching.In the second instance, the sheets must have one surface grained andpolished with hard, flint balls or marbles, and fine abrasives to renderthe surface porous, i. e., receptive to wetting by Water and ink and tothe very slight absorption of these materials, since this property is anessential requirement for metal plates used in the lithographic processof printing. In both cases it is necessary to have a rolled zinc sheetor plate with sufficient hardness and toughness to resist wear anddeformation. For example, in the case of zinc plates used forphoto-engraving, theimage developed in relief may project above theetched surface of the metal from three to ten 5,, thousandths of an inchin half-tone cuts, and up to thirty thousandths of an inch in line cuts,and the small pin point dots in the highlights of a half-tone etchingand the fine lines in a line out may be only a few thousandths of aninch in): in width.

Where the zinc etchings are used in newspaper work and similar types ofprinting, the raised surface of these plates are subjected to greatpressure in the course of the stereotype mat molding operation wherein asheet of specially prepared thick paper board, slightly dampened, ispressed into the surface of the zinc etching by means of a platen typeor roller type press, in which pressures as high as 4000 pounds persquare inch are sometimes reached. The paper mat after drying is removedfrom the zinc etching and then serves as a mold into which moltenstereotype metal is cast. Since several mats are usually required fromeach zinc etching, this molding pressure is applied to the etching anumber of times and in the case of zinc etchings for syndicated printedmatter the number of mats required and the number of times the pressureis applied may run as high as 200 or 300. The zinc sheet therefore mustpossess sufficient hardness and strength to resist the repeatedpressures of the molding operation, without the raised surfaces of theplate being crushed or distorted to any serious extent; otherwise lossof detail will result in the printed image.

Furthermore, the zinc plates are frequently heated to a temperatureapproximating 600 F. in the course of developing an acid-resisting topwith the so-called hot top type of photosensitive enamel, and they mustalso be heated anywhere from 8 to 16 times to a temperature ofapproximately 300 F. to set or burn in the dragons blood powder used asan acid resist in the etching process. In the course of these Variousheating operations, the zinc plate is softened somewhat, the drop inhardness depending upon the temperature to which the plate is heated andthe number of times it is subjected to the heating operation. Thissoftening or annealing of the plate makes it less resistant to crushingunder the pressures used in mat molding and less resistant to wear also.For example, an ordinary grade of rolled zinc used for the production ofphoto-engraving will have an original Rockwell hardness of the order of65, and a hardness of approximately 4.5 to 50 after being subjected tothe various heating operations as described above.

Heretofore, in using the ordinary grade of photo-engraving zinc,photo-engravers have found it difficult, if not practically impossible,to maintain fine lines or dots in the zinc etching when the mats aresubjected to the high molding pressures used in the so-called dry matprocess, particularly if a number of mats had to be made from a givenetching, as in the case of syndicated printed matter. To obviate thisdifficulty it is the practice either to make a number of zinc etchingsof a given image so that a new zinc etching could be substituted for theold ones as they break down in the molding operation, or to resort tothe use of the much more expensive engraving plates made of copper,brass, or other alloys, which possess greater resistance to de-vformation under the stresses imposed upon them by the molding operation.

Where printing is done directly from the zinc etchings, it is alsonecessary that the zinc possess suiiicient hardness and resistance towear and deformation, so that the etched image does not crush down orwear off under the repeated application of pressure when the surface ofthe paper is brought in contact with the ink surface of the zinc etchingin the action of the printing press, and also to withstand the abrasiveor wearing action of the paper as it rubs against the zinc surface inthe printing process.

The principal objects of the invention are to overcome theaforementioned difliculties; to provide a zinc base alloy capable ofbeing rolled or otherwise formed into plates or sheets which possess agreater hardness and superior resistance to deformation and wear underthe conditions to which they are subjected. in their use in the variousbranches of the printing industry; and to provide a zinc base alloywhich will undergo a loss of hardness, after being subjected to thevarious heat treatments, which is materially less than that of the zincplates heretofore used.

Further objects will be apparent from a consideration of the followingdescription which discloses different examples illustrative of theinvention.

I have found that a zinc plate or sheet possessing the aforementionedcharacteristics can be produced by alloying commercial zinc with a smallpercentage of one or more of the metals of the alkali metal group(sodium, potassium, lithium, etc.) and/or the alkaline earth group(magnesium, calcium, barium, etc.). For example, the zinc base may bealloyed with small percentages of magnesium or lithium to produce aplate or sheet having a greater hardness and superior resistance todeformation and wear than the ordinary zinc', regular commercial grade,photo-engravers plates, and if in addition to the magnesium or lithiumsmall percentages of other alkali metals, such as sodium or potassium,or alkaline earth metals, such as calcium or barium, are incorporated, afurther increase in hardness and resistance to deformation and wear isproduced.

Although the relative percentages of the different alloying constituentsmay be varied, I have found that it is highly desirable, if notessential for the production of commercially satisfactory plates, thatthe relative amounts of certainof the alloying elements be carefullycontrolled and held below maximum limits, since amounts of the alloyingelements in excess of such limits are quite apt to result either in theformation of inclusions which show up on the etched surface of thetreated plate, or in the formation of defects which interfere with theetching and burning-in operations.

A satisfactory alloy is produced using a commercial zinc base(containing as impurities approximately 0.2 to 0.4% cadmium, 0.01 to0.02% iron, and 0.2 to 0.3% or more lead), and alloying the zinc base,with sufficient lithium or magnesium to produce in the finished alloyfrom 0.002 to less than 0.005% lithium and/or similar amountsofmagnesium; or by alloying the zinc base with either lithium or magnesiumand sufficient barium or calcium to produce an alloy containing from0.002 to 0.01% barium or calcium, or with sufficient sodium or potassiumto produce an alloy which will contain from 0.002 to 0.01% sodium orpotassium; or by alloying the zinc base with lithium or magnesiumtogether with any one or more of the other elements, in amounts withinthe above specified limits.

In preparing a zinc alloy in accordance with the present invention, anyof the usual methods of alloying may be used, it being understood thatany suitable apparatus or procedure may be adopted as long as thecomposition or alloy produced possesses the characteristics herein setforth. In accordance with the preferred procedure, the zinc base isfirst melted in a crucible or other suitable apparatus, and ismaintained at a temperature sufficient above its melting point(approximately 800 to 900 F.) to permit easy incorporation of thealloying ingredients, which may be in the form of a master alloy ofpredetermined composition, such, for 'example, as a calcium-zinc masteralloy, a magnesium-zinc master alloy, etc. As the metals of both thealkali and alkaline earth groups possess a deoxidizing effect on themolten zinc, and as some of the more reactive metals may undergovolatilization, there are apt to be slight losses due to deoxidizing themolten zinc and volatilization, and hence it may be necessary ordesirable either to add an excess sufficient to compensate for suchlosses, or to incorporate other metals of the same groups so as toinsure the retention of a sufiicient amount of the alloying elements toeffect the desired hardness. Since the percentage of the alloyingelements are so low that in many cases they Would be reported by anordinary analytical chemist as traces, it is necessary, in analyzingsuch alloys, to determine the alloying constituent by a spectroscop-e orother means capable of determining such small amounts.

The following example is illustrative of a preferred procedure formaking a zinc-magnesiumcalcium alloy:

Example 1. Magnesium-caZcz'um-zinc alloy 1000 pounds of zinc, containingnot more than approximately 0.60% cadmium, 0.025% iron, and 0.60% lead,but preferably having a composition within the range of cadmium0.25-0.30%, iron 0.015-0.020%, lead 0.304135%, was first melted in agraphite crucible, and after the metal was entirely molten, the surfaceof the bath was skimmed to remove any accumulation of dross or oxide.While maintaining the bath at a temperature of between 800 and 900 F., 6pounds and 1.1 ounces of a calcium zinc master alloy, containing 0.6% ofcalcium, was then added and throughly incorporated in the molten bath.After adding the calcium alloy, 9 ounces of a magnesium-zinc masteralloy, containing 5.25% magnesium, was then added and thoroughlyincorporated. A calculated analysis of the alloy showed 0.002 to 0.003%magnesium and 0.004% calcium. Rockwell hardness tests of the alloyshowed an average. hardness of 86 before heating and an average hardnessof 74 after heating four minutes at 600 F., as compared with an averagehardness of 76 before heating and an average hardness of 55 afterheating, for a regular commercial grade (soft) photo-engravers plate.

Further examples are as follows:

Example. 2. M agneszum-sodium-zmc alloy One thousand pounds ofcommercial zinc of the same composition as set forth in Example 1 wasalloyed with 9 ounces of a magnesiurmzinc master alloy containing 5.25%magnesium and 2 pounds 8 ounces of a sodium-zinc master alloy containing2.0% sodium. A calculated analysis of the resulting alloy gave amagnesium content of 0.003% in gnesium and 0.005% sodium. Rockwellhardness tests showed an average hardness of 86.5 before heating and anaverage hardness of '74 after heating.

Example 3. Magnesium-sodium-einc alloy Example 4. Magnesium-barium-zincalloy One thousand pounds of commercial zinc of the same composition asset forth in Example 1 was alloyed with 9 ounces of a magnesium-zincmaster alloy containing 5.25% magnesium and 5 pounds 9 ounces of abarium-zinc master alloy containing 0.9% barium. A calculated analysisof the resulting alloy showed a magnesium content of 0.003% and a bariumcontent of 0.005%. Rockwell hardness tests showed an average hardness of86 before heating and 73.5 after heating.

Example 5. M agnesium-barium-zinc alloy One thousand pounds ofcommercial zinc of the same composition as set forth in Example 1 wasalloyed with 9 ounces of a magnesium-zinc master alloy containing 5.25%magnesium and 11 pounds 2 ounces of a barium-zinc master alloycontaining 0.9% barium. A calculated analysis of the resulting alloyshowed a magnesium content of 0.003% and a barium content of 0.01%.Rockwell hardness tests showed an average hardness of 85.5 beforeheating and 76 after heating.

Ermmple 6. M agnesium-barium-sodium-zinc alloy One thousand pounds ofcommercial zinc of the same composition as set forth in Example 1 wasalloyed with 9 ounces of a magnesium-zinc master alloy containing 5.25%magnesium, 11 pounds 2 ounces of a barium-zinc master alloy containing0.09% barium, and 5- pounds of a sodium-zinc master alloy containing2.0% sodium. Analysis of the resulting alloy showed a magnesium contentof 0.003%, a barium content of 0.01 and a sodium content of 0.01%.Rockwell hardness tests showed an average hardness of 86.5 beforeheating and 73.5 after heating.

Numerous other experiments have been conducted with zinc base alloyscontaining varying percentages of sodium, calcium and barium in amountswithin the ranges above specified, and the resulting alloys showed ahardness before and after heating considerably greater than that of theregular commercial grade (soft) photo-engravers plate.

Alloys made in accordance with the present invention may be rolled orotherwise formed into sheets or plates for both photo-engraving andlithographic reproductions, and the sheets may be grained to produce asurface which can be easily wet with water and ink and which will retaina thin film of these materials, as required in lithographic printingprocesses. Although the graining operation produces a toothed surface inwhich the difference in elevation between the highest and lower pointsamounts to only four to five ten-thousandths of an inch, the fine toothor grain is retained substantially intact during the entire run of theplate, due to the increased hardness and greater resistance todeformation and wear inherent to an alloy made in accordance with thepresent invention.

While I have described different desirable embodiments of the invention,it is to be understood that this disclosure is for the purpose ofillustration, and that various changes and modifications of proportions,etc., may be made without departing from the spirit and scope of'theinvention as set forth in the appended claims.

I claim:

1. A zinc base alloy having a high hardness and superior resistance todeformation and wear, said alloy containing 0.002 to 0.03% of a metalselected from a group consisting of magnesium and lithium, and 0.002 to0.01% of a metal selected from a group consisting of sodium, calcium andbarium, the remainder, except for minor impurities, being zinc.

2. A zinc base alloy having a high hardness and superior resistance todeformation and wear, said alloy containing 0.002 to 0.03% magnesium,and 0.002 to 0.01% of a metal selected from a group consisting ofsodium, calcium and barium, the remainder, except for minor impurities,being zinc.

3. A zinc base alloy having a high hardness and superior resistance todeformation and wear, said alloy containing 0.002 to 0.03% of a metalselected from a group consisting of magnesium and lithium, and 0.002 to0.01% of a binary alloy of metals selected from a group consisting ofsodium, calcium and barium, the remainder, except for minor impurities,being zinc.

4. A zinc base alloy having a high hardness and superior resistance todeformation and wear, said alloy containing 0.002 to 0.03% magnesium,

and 0.002 to 0.01% of sodium, the remainder, .1

except for minor impurities, being zinc.

5. A zinc base alloy having a high hardness and superior resistance todeformation and wear, said alloy containing 0.002 to 0.03% magnesium,0.002 to 0.01% sodium, and 0.002 to 0.01% barium, the remainder, exceptfor minor impurities, being zinc.

WILLIAM H. FINKELDEY.

